AN1623 Datasheet, PDF (1/6 Pages) STMicroelectronics – REGULATION LOOPS PRECISION CALCULATION

AN1623
APPLICATION NOTE
TSM1011:
REGULATION LOOPS PRECISION CALCULATION
1 PRINCIPLE OF OPERATION
This technical note shows how it is possible to
calculate the current and voltage precision in the
regulation loop of the TSM1011.
The TSM1011 is a highly integrated solution for
SMPS applications requiring CV (Constant
Voltage) and CC (Constant Current) mode.
The TSM1011 integrates one voltage reference
and two operational amplifiers (with ORed outputs
- common collector).
by Giuseppe SCUDERI
The voltage reference combined with one
operational amplifier makes it an ideal voltage
controller.
The other operational amplifier, combined with
few external resistors and the voltage reference,
can be used as a current limiter.
This circuit is designed for use in battery chargers
with a constant voltage and a limited output
current and in adapters.
It can be used in every type of application
requiring 0.5% and 1% voltage reference
precision fixed at 2.5 Volts.
Figure 1 : Typical application using TSM1011 inSSMPS
PWM
controller
D2
C1 C2
Rlimit
TSM1011
Vref
1
2,5V
CV+
5
R4
CC+
3
8
Vcc
28V
CV
Out
7
4
CC
CV-
optocoupler
secondary side
OUT+
R3
R2
Rvc1 Cvc1
C3
optocoupler
primary side
R5
CC-
Gnd
2
6
R1
Cic1
Ric2
Ric1
D1
Rsense
OUT-
1.1 Voltage Control
The Voltage Control loop is controlled via a first
transconductance operational amplifier, the
optocoupler which is directly connected to the
output and an external resistor bridge connected
between the output positive line and the Ground
reference.
The middle point is to be connected to the CV- pin
of TSM1011, and, if R₂ is the upper resistor, and
R₁, the lower resistor of the bridge, the
relationship between R₂ and R₁ value should be
chosen as written in Equation 1:
( ) V_lim = f R₁,R₂, V_ref
V_lim
=
V_ref
R₁ + R₂
R₁
Equation 1
where V_lim is the desired maximum output
voltage.
When under constant voltage control mode, the
output voltage is fixed thanks to the R₁/R₂ resistor
bridge. To avoid the discharge of the load, the
resistor bridge R₁, R₂, should be highly resistive.
November 2002
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